keith gray, ilm
TRANSCRIPT
Cost Benefit of Pre‐Dredging Investigations
By Keith GrayApril 5, 2012
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“An expert is a person who has made all the mistakes in a very narrow field.”Niels Bohr
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“All we have in the budget is $7,500 –Do what you can.”
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Budget• Operator $75/hr. X 9 hrs. → $675• Labor $55/hr. X 9 hrs. → $495• Machine (Day rate) → $900• Dewatering bag → $400/day• Total → $2,470/day
No mob/de‐mobLet sediment dry, spread it,seed it
3 Days!
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What did it cost us beyond 3 days of activity?
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Truxor: 3 days @ $2,500/day = $7,500
• Labor to cut bag and spread $200• Bobcat rental $300• Tow truck for bobcat $140• Silt fence $200• Labor $300Total $1,140
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• Bobcat rental (Day 2) $300• Labor $300• Grass / cover crop seed $60Total $660
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• Top soil $200• Seed $60• Labor $260
Total $520
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• Goose protection fencing $160• Seed $60• Labor $280
Total $500
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• 1st try by hand $200• 2nd try (Bobcat) $1,140• 3rd try (Bobcat V‐2) $660• 4th try (Top soil) $520• 5th try (Goose fencing) $500
Total $3,020
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Spring 2013
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“I thought you’d have removed a lot more than that for $7,500!”
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Mistakes Made
• Understand the material you are working with:–Removal rate–Material handling–Wet vs. dry volumes
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Mistakes Made
• Consider secondary use & associated costs:–Will it support growth?–Will it dry?–Will it erode easily?–Contaminated?
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Mistakes Made
• Establish realistic client expectations:–Volume–Appearance–Project duration
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“Learn from others mistakes. You don’t live long enough to make them all yourself.”
Eleanor Roosevelt
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How much to dredge my pond?
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Dredging Feasibility Study
$1,500 to $10,000
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“Just tell me how much sediment I have”
“We want as much of our money to go into removing sediment as possible.”
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Bathymetric Map
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15,600 CY
15,600 CY X $20 ‐ $40/CY = $300,000 to $600,000
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Other Costs:
• Disposal• Loading• Analysis• Repair to work areas• Permits• Bonding
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Dredging Feasibility Study:
• Understand the goals/needs of the client.• Evaluate the options to achieve clients needs.
I. Recreation Boating swimming
II. Water Quality Plants Algae clarity
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III. Fishery Habitat Depth
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Main Inlet 2.8 acresSediment Mapped Area Avg. thickness Volume Percentthickness ft2 ft ft3 of volume5 ft + 2,049 5.3 10,858 8.2%4 ‐ 5 ft 929 4.5 4,181 3.2%3‐ 4 ft 2,122 3.5 7,428 5.6%2 ‐ 3 ft 10,157 2.5 25,394 19.2%1 ‐ 2 ft 29,967 1.5 44,950 34.0%0 ‐ 1 ft 78,516 0.5 39,258 29.7%
132,069 total volume ft3
4,891 cubic yards
47,861 ft3 = 1,773 CY @ $50/CY = $88,000+ Hauling and disposal$160/load x 90 loads = $14,400
~ $100,000
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Pre‐Dredging Investigation Benefits:
• Determine sediment distribution• Determine sediment type
– secondary use– Disposal– compaction
• Identify high priority areas• Identify source of sediment
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Pre‐Dredging Investigation Benefits:
• Determine the most effective method of removal (hydraulic, wet mechanical, dry mechanical).
• Identify qualified contractors and use information gathered to create a bid package.
• Options for removed sediment.
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“Dredging Feasibility Study”
A good investment.
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